1. Field of Invention
This invention relates generally to systems and methods for preserving stored foods and, more specifically, to a system and method for preserving stored foods utilizing a high concentration ozone generation apparatus.
2. Background of the Invention
The protection of food from damage caused by microbes, spores, insects and other similar sources is a major concern. Each year, economic losses of food and fiber due to damage from such sources is more than $122 billion. Currently, food items are preserved using a variety of methods, including fumigation with toxic chemicals, irradiation, biological control, heat exposure, and controlled atmosphere storage (a fruit industry technique that involves modifying the concentration of gases naturally present in the air). Certain of these methods, including for example fumigation and irradiation, carry risks for workers involved in the treatment and/or for consumers of the preserved food.
The use of ozone, an unstable molecule comprised of three atoms of oxygen (O3) having a high oxidation potential, to purify water and air is well known. It was used to purify drinking water by the latter part of the 1800""s, and today is used for this purpose by most major U.S. cities. Ozone has also been utilized for the purification of other types of water, including irrigation water, as well as waste water and cooling tower water.
The use of ozone as a microbicide and odor reducer is not, however, limited to the treatment of water. While ozone is highly water soluble and thus generally more effective in water, it can be used effectively in the air as wellxe2x80x94attacking yeasts and fungi as well as bacteria. In this regard, for nearly a century, ozone has been used as a food preservation agent for a wide variety of perishable food items. Food items potentially preserved by ozonation include potatoes, eggs, cheeses, bananas, berries, meats, carrots, onions, and peaches. (Ozone dissolved in water has also been used in food storagexe2x80x94including for the preservation of fish in ozonated ice.)
The basic principles underlying the use of ozone generation are well established. Clean, dry air consists of approximately 78 percent nitrogen gas (N2), approximately 21 percent oxygen gas (O2) and less than one percent of hydrogen (H2) and other gasses. When air (referred to as the xe2x80x9cfeed gasxe2x80x9d in this context) is irradiated using either an ultraviolet source or corona discharge (the acceleration of electrons between two electrodes, separated by a dielectric material, to collide with a feed gas passed therebetween), some of the O2 molecules are split to form two short-lived oxygen atoms. These oxygen atoms combine, almost instantaneously, with uncleaved oxygen molecules to form ozone. Ozone and certain of the other atoms and molecules formed as a result of ozonation (including hydrogen peroxide and hydroxyl radicals) have a number of beneficial uses in the areas of disinfection and odor eliminationxe2x80x94and for this reason are useful in preserving foods.
Ultraviolet radiation is disfavored as a method for generating ozone, due to the inability to produce high quantities of ozone at a relatively low cost in this fashion. As a result, most commercial ozone production is accomplished using a corona discharge type of ozone generator.
However, there are numerous problems with prior art corona discharge ozone generators, and thus limitations on their suitability for use in a system and method for preserving stored foods. Thus, when the feed gas is passed between the electrodes, water or dust present in the feed gas attach themselves to the dielectric surrounding the cathode. These spots tend to attract electrons, with the result that hot spots are formed on the surface of the dielectricxe2x80x94leading eventually to the burning through of the dielectric and consequent failure of the generation apparatus. In the commercial area, ozone generators require constant servicing and, indeed, rebuilding, because of such problems. In the City of Los Angeles, for example, high concentration ozone generators used to treat the city""s drinking water are presently required to be rebuilt after approximately ten days of usexe2x80x94a rate that is plainly undesirable. Moreover, prior art devices do not permit the ready manipulation of the ozonation products, for example to produce more ozone and less nitrogen-containing compounds as is particularly beneficial for the preservation of stored foods.
U.S. Pat. No. 4,954,321, issued to the applicant herein, illustrates a plasma corona discharge apparatus, representing an improvement upon the basic corona discharge process. Generally, a plasma corona discharge apparatus is similar to a non-plasma apparatus, except that in a plasma apparatus, an inert gas is inserted into an elongated, insulated, sealed cathode, into which electrons are fired for the ozonation process. That gas performs two functions. First, it generally precludes the formation of hot spots and resulting dielectric burn-through and generator failure through a convection process. In this regard, the inert gas, which has become a plasma by virtue of the electrons passing therethrough, becomes attracted to a water or dust spot, the gas becomes heated and then rises away from the hot spot, to be replaced by gas having a lower temperature. This results in a relatively constant movement of the gas and substantially reduces overheating and/or apparatus failure attributable to the formation of stable hot spots.
The second function of the inert gas is to directly assist in the efficiency of the ozonation process. In this regard, upon the firing of electrons from an electron gun into the inert gas, a plasma is formed within the cathode (i.e., on the inside of the dielectric), and also outside of the dielectric. The passage of electrons though this plasma and into the feed gas causes oxygen disassociation and reformation as ozone at an improved rate over non-plasma devices.
However, even the plasma device illustrated in U.S. Pat. No. 4,954,321, while more reliable than prior art devices, suffers from important limitations and deficiencies. For example, the energy produced by the electron gun firing into the cathode is concentrated near the electron gun, and gradually dissipates over the length of the electrode. This results in a decrease in the effectiveness of this particular prior art apparatus in treating the feed gas, and thus in the production of a lower concentration of ozone than is possible if the energy level could be maintained constant throughout the length of the cathode.
A need therefore existed for an improved system and method for preserving stored foods, preferably based on an ozone generator apparatus and method capable of reliably generating high concentrations of ozone (and other ozonation products) suitable for use in such treatment. The improved system and method should provide for the maintenance of a relatively constant energy level throughout the length of the energy-producing electrode, so as to provide more efficient production of ozonation products. The improved system and method should also provide for the efficient adjustment of the products of ozonation, so that ozone and other oxidizing products can be favored. The improved system and method should not adversely affect the taste of the treated food product, and should not create any harmful byproducts. The present invention satisfies these needs and provides other, related, advantages.
It is an object of the present invention to provide an improved system and method for preserving stored foods with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons.
It is an object of this invention to provide an improved system and method for preserving stored foods with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons, wherein the system and method have a reduced risk of failure as compared to prior art systems and method based on corona discharge apparatuses.
It is a further object of this invention to provide an improved system and method for preserving stored foods with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons capable of producing a higher concentration of ozone than prior art systems and methods based on corona discharge apparatuses by, among other things, providing for a substantially constant energy level throughout the length of the first electrode in the apparatus used in the system and method of the present invention.
It is a still further object of this invention to provide an improved system and method for preserving stored foods with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons which system and method may be readily adjusted to alter the relative quantities of atoms and molecules produced from the bombardment, so as to produce fewer nitrogen containing compounds and greater quantities of ozone and other oxidizers.
In accordance with one embodiment of the present invention, a system for preserving stored foods is disclosed. The system comprises, in combination: an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode; wherein said first electrode comprises: an electron gun coupled to a power source and located proximate one end of said first electrode; a rod in electrical communication with said electron gun; a first tube of dielectric material disposed along a length of said rod; a second tube of dielectric material dimensioned to receive therein said first tube; wherein said second tube is substantially sealed; and an inert gas disposed within each of said first tube and said second tube; a second electrode containing a channel dimensioned to receive therein said first electrode so that sufficient space is present between said first electrode and said second electrode that a feed gas may be passed through said channel along an exterior surface of said first electrode; a feed gas inlet coupled to said second electrode and wherein said feed gas inlet is in communication with said channel; and a feed gas outlet coupled at a first end thereof to said second electrode and wherein said feed gas outlet is in communication with said channel; means coupled to said feed gas outlet for transporting said feed gas to a food storage area.
In accordance with another embodiment of the present invention, a system for preserving stored foods is disclosed. The system comprises, in combination: an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode comprising a substantially sealed tube of dielectric material; wherein said first electrode further comprises: a first electron gun coupled to a power source, located proximate one end of said first electrode, and adapted to fire electrons into said substantially sealed tube of dielectric material; a second electron gun coupled to a power source, located proximate a second end of said first electrode, and adapted to fire electrons into said substantially sealed tube of dielectric material; and an inert gas disposed within said substantially sealed tube of dielectric material; a second electrode containing a channel dimensioned to receive therein said first electrode so that sufficient space is present between said first electrode and said second electrode that a feed gas may be passed through said channel along an exterior surface of said first electrode; a feed gas inlet coupled to said second electrode and wherein said feed gas inlet is in communication with said channel; and a feed gas outlet coupled at a first end thereof to said second electrode and wherein said feed gas outlet is in communication with said channel; and means coupled to said feed gas outlet for transporting said feed gas to a food storage area.
In accordance with still another embodiment of the present invention, a method for preserving stored foods is disclosed. The method comprises the steps of: providing an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode; wherein said first electrode comprises: an electron gun coupled to a power source and located proximate one end of said first electrode; a rod in electrical communication with said electron gun; a first tube of dielectric material disposed along a length of said rod; a second tube of dielectric material dimensioned to receive therein said first tube; wherein said second tube is substantially sealed; and an inert gas disposed within each of said first tube and said second tube; a second electrode containing a channel dimensioned to receive therein said first electrode so that sufficient space is present between said first electrode and said second electrode that a feed gas may be passed through said channel along an exterior surface of said first electrode; a feed gas inlet coupled to said second electrode and wherein said feed gas inlet is in communication with said channel; and a feed gas outlet coupled at a first end thereof to said second electrode and wherein said feed gas outlet is in communication with said channel; providing means coupled to said feed gas outlet for transporting said feed gas to a food storage area; providing power from said power source to said electron gun; passing a feed gas into said feed gas inlet, through said channel, and out of said feed gas outlet; transporting said feed gas through said means to said food storage area.